Superheater element for smoke-tube boilers



Jwiy 3Q, 1935. H. FRANK SUPERHEATER ELEMENT FOR SMOKE TUBE BOILERS FiledJan. 24, 1935 INVENTOR #525527" FRm/K. BY 0 .IATToNEY Patented July so,1935 2,009,883

UNITED STATES PATENT OFFICE SUPERHEATER ELEMENT FOR SMOKE-TUBE BOILERSHerbert Frank, Cassel-Wilhelmshohe, Germany, assignor to The SuperheaterCompany, New York, N. Y; I

Application January 24, 1935, Serial No. 3,220

r In Germany May 19, 1933 13 Claims. (01. 122-462) .This inventionrelates to a superheater element tion, its gist resides in the discoverythat in Order which is intended for use in a flue of a fire-tube t taithe h h r s p a temperature boiler and consists of a plurality ofparallel or int nd d it s quis t t p v d f a Certain practicallyparallel tubes r portions of tubes correct relation between thesectional area of the connected'with one another in such a manner assteam p the superheating surface and the to form-a continuous path inwhich the steam sectional area of the smoke passage. The invenflows toand fro. The object of th i ti 1 tion contemplates obtaining thisrelation in such to increase the superheating capacity of the a a r th wth ut a y at ria n r as f superheater so as to increase correspondinglythe the superheating Surface a suitable distribution superheatingtemperature of the steam, without O this surfaee, and 0f the sectionalarea of the 10 any undesired fall of pressure of the steam in the Steampassage in the f and at the same time an superheating elements and lossof draught in the accommodation of th speed o q t m to th lines of theboiler. r g changes-of the temperature of the smoke gases, is If, as hasgenerally been customary up to; now, rendered possible it is endeavoredto obtain an increase of the W, the invention resides in h h l p 15superheating temperature solely. by an increase heating t, as re a thesectional area! C of the superheating surface, the loss of draught isits st a passa is d v d into threezenee, increased if the diameter ofthe'flues or the numviz. a first zone having a large sectional area, ither of the same remains the some as before In second zone followingimmediately said first zone order to obviate this it would be necessaryto inand having a materially mall r se t nal area 20 crease either thesectional area of the gas pasand being at east'twicesubje d t0 h acsage, that is to say, the diameter of the flues, or of the smoke gasesstreaming through flue the number of these tubes hi h, however, would inthat zone thereof where said gases are hottest, in either caseentaildifliculties in view ofthe red a third m having a lar nal r .strictedspace available in fire-tube-.boilers, for and serving chiefly forconducting away the superf instance those of locomotives, heated steam.'Besides this, a particular, feature In order to pa regard t th increaseof t of the whole is that the individual zones of the specific volume ofthe st th t takes place element are so arranged inthe flue that the freewhen the steam is superheated, it has already sectional area of the gaspassage remains er been, proposed to increase the sectional area of prat ca y the same along e e i e length of 30 theisteam passage in thesuperheating tubes fr the flue or increases only a little in thedirection the entrance end to the exit end of the same, and of the smokegases, the s tio po tions bealsothe reverse way has been proposed; vjz ttween the different sectional areas being located decrease said s ti larea, from t entrance either in the plane of section of the flue orwhere end to the exit end inorder. to increase thereby there areversinsbends of the heating tube 3.5

the speed of the steam. j w within the flue.

,Still another proposal is this to give the supery invention isillustrated diagrammatically heating tubes a smaller sectional area inthat andbyway 0f eXample 0n theaeeempanying d zone where the smoke gasesare hottest, the i ing on which Figure l is an axial section throughtention being to increase the speed of the steam a flue provided with asuperheating element dein this zone and to obtain an im roved tr signedaccording to this invention, this element mission of the heat from saidgases to the steam, being shown in side-View, and Figures 4 a d A thusdesigned superheating element consists, 5 a Similar representationsshowing four m d therefore, of a portion having a large sectionalfications, all asful y described a te area in that zone of the fluewhere the tempera- In the constructional form illustrated in Figture ofthe smoke'gases is comparatively low, and ure 1, the numeral 2 denotesthe flue, the right of a portion having a smaller sectional areain handend of which communicates with the thatzone where the temperature of thesmoke smoke-chamber, in the upper portion of which gases is highest,this portion comprising preferthe steam chest (not shown) is locatedfrom ably a plurality of narrow tubes. which the .wet steam isdistributed to the various All those proposals have, however, not provedsuperheating elements, whereas the left-hand suitable for the purpose inview, as the respective end of the flue communicates with the fire-box.designers had failed to, discover the only suc- The wet steam passesfirst through the tube porcessful solution of the problem. This solutiontion I which has a sectional area as large as pos- 4 forms the subjectmatter of the present invensible. The steam passes then in the .samedirecthe tube portion 8 through which the superheated steam is conductedaway being as large as possible.

In Fig. 2 the tube portions l and I4 correspond practically with thetube portions l and 8 of Fig. 1, and the tube portion ll correspondspractically with the tube portion 4 but between the tube portions l9 andII of Fig. 2, the steam path is formed by two tubes or tube portions 9which are connected up in parallel to the tube portion ID, as well as tothe tube portion l I. The united sectional areas of said tubes 9 of thefirstsection is smaller than the sectional area of the tube portion '19thereof, and the sectional area of the tube portion 1 I of theintermediate section is smaller than the combined sectional area of thetubes 9, thus correspondingwith the tube portions 3 and 4 of Fig'. 1.The loops l2 of Fig, 2 and the tube portions I3 and I4 of the thirdsection in Fig. 2 correspond practically with the loops 5 and the tubeportions 6, l and 8 of Fig. l, as regards their sectional area.

In Fig. 3 is shown a constructional form intended especially. for smallflues. The subdivision of the steam path is in this modificationextended not so far as in Figs. 1 and 2, in that there is only one loop21 located between the tube portions 291 and 28. The two tube portions26 correspond practically'with the tube portions 1 and 8 of Fig. 1, butthey are longer; they may have equal sectional area, which, however, isto be larger than thatlof the loop 21 and of the tube portion 28 whichmay likewise be regardedas a loop. The sectional area of the tubeportions 29 and 28 is smaller'than that of the tube portions 26, and thesectional area of the loop 21 is smaller than that of said tube portions29 and 28, always inaccordance with the principle of the invention. V 1

In Fig. 4 the subdivision of the steam path is as in Fig.3 also lessthan in Figs. 1 and 2, but while in Fig. 3 the loop 21 is formed of onlyone tube or tube portion there are'in Fig. 4 several loops 25 connectedup in parallel to parallel tube portions 23 and 24. The parallelportions 23 of the first section communicate with the entrance tubeportion 2| and the parallel portions 24' of the third sectioncommunicate with the delivery tube portion 22. thereof. These endportions 2| and 22 may have equal sectional areas. Also the tubes 23have equal sectional areas, as have also the loops 25 and theitubes 24,the sectional area of said loops 25 being the smallest of thesuperheating element. The loops 25 are located in that zone of the fluewhere the fire gases are hottest.

Finally, in Fig. 5 the wet-steam supplied to the superheating elementpasses first through two parallel pairs of comparatively-short tubes,each pair comprising in turn two'parallel tubes !5 and IS, the unitedsectional area of which is less than the sectional area of the supplytube. Said tubes l5 and iii are located in the proximity of the exit endof the flue. 'At their other end said tubes communicate with two tubesor loops I! and [8 each having a' sectional area which is superheatingelement.

As shown in the drawing the transitions from one section of asuperheater element to another section may be located in the flues atthe places where the direction of the steam flow is reversed; or asshown for example in Figure 3 the transitions between the sections 21,28 and 28, 26 respectively are located in alignment with each other andsubstantially in the same sectional plane or transverse section throughthe flue. As a result of these arrangements as variously shown in theseveral modifications, the free sectional area of the gas passageremains practically the same over the length of the flue or increasesonly a little progressively in the direction of the gas flow to the exitend of the flues. Preferably the transitions between the severalsections of a superheater element are made in slight steps for retainingthe pressure drop of the steam as small as possible.v

In order to respond to the requirement to make the fall of pressure ofthe steam within the superheater as small as possible it is desirable tomake the sectional area of the steam passage at the exit end of thesuperheating tube, where the specific volume of the steam is thegreatest, larger than the sectional area of the steam passage at theentrance end of said tube. However, constructive considerations renderit advisable in many cases to make the sectional area at the entranceto, and the exit from, the steam passage equally large. The change ofthe sectional area of the steam passage may take place in the individualzones either in several abrupt steps, as shown in the drawing, orgradually along the'same. Furthermore, the tubes in the individual zonesor sections may be individual ones (as shown in all zones in Figures 1and 3 orv as 12, I3 I4, Figure 2 or [9, Figure 5) or may comprise aplurality of tubes connected up in parallel, (as at 9 in Figure 2, 23,25, 24 in Figure 4, or at l5, l6, l8 in Figure 5). Finally, it isadvantageous for the purpose in 'view to provide at the place of thehottest fire gases a larger heating surface presented by tubes with thesmallest sectional areafor the steam passage.

It should be noted that with superheating elements designed according tothis invention, the

sectional area of the gas passage in the flue remains either practicallythe same along the entire length of the flue or increases onlyimmaterially in the direction to the smoke chamber. Consequently, thesudden reduction of the speed of the gas current that would otherwiseoccur within the flue is obviated and also the risk of the formation ofa deposit of soot and fiue dust at this place is considerablydiminished. If the speed of the gas current in the direction to thesmoke chamber becomes lower, that is to say, if it is highest at thefirebox, then this will be most favorable for the'heat transmission, asjust at this place thelargest superheating surface'is located throughwhich 'the steam flows with the highest speed. There is, furthermore,obtained in the flues an average hydraulic depth considering the lengthof the tube that is essentially equal to the hydraulic depth of theheating tubes.

If one endeavors to obtain the higher superheating of the steam merelyby'an increase of the superheating surface, as has previously been done,then the hydraulic depth in the lines will be considerably smaller thanthatin the heating tubes. With equal loss of draught in two bundles oftubes the speed of flow depends only upon the hydraulic depth, inconsequence whereof the heating gases are deflected in a greater measuretothose However, by making use of a superheating element designedaccording to the present invention the over-all efflciency oi thesuperheater is improved. This is true especially of so-called smalltubesuperheaters, that is to say, of superheaters for boilers with flues ofa smaller diameter. The improvement of the over-all efliciency is, insuch a case, rendered possible on the one hand by the improvement of theratio of the heating surfaces located in the proximity of the firebox(this ratio of heating surfaces being that between the superheatingsurface and the evaporative heating surface) and on the other hand bythe improvement of the ratio used in equipping the flues withsuperheating tubes (ratio between the number of the fines and the numberof the heating tubes) By the term over all efliciency I mean the resultattained by properly relating the ratio of the heating surfaces to theratio between the hues and the heating tubes, that is to say, thosetubes which have superheating tubes and those tubes which have nosuperheating tubes. Owing to the favorable distribution of the steamspeed along the path of the superheated steam, flues of a smallerdiameter can be used.

I claim:

1. A superheater element for use in a flue of a smoke tube boilercomprising a plurality of interconnected, parallelly disposed tubularportions of different diameters extending forwardly and backwardly inthe flue and constituting an inlet section, an outlet section and anintermediate section of smaller diameter than both said inlet and outletsections and having the greater part thereof located in that part of theflue which lies adjacent the fire-box, the tubular portions constitutingthe superheater element being positioned with respect to each other inthe flue to locate certain contiguous tubular portions of differentdiameters parallel to other tubular por tions having diameters sorelated to those of said certain portions as to offset changes in thediameter of said element along the flue.

2. A superheater element for use in a flue of a smoke tube boilercomprising a plurality of interconnected, parallelly disposed tubularportions of different diameters extending forwardly and backwardly inthe flue and constitutingan inlet section, an outlet section and anintermediate section of smaller diameter than both said inlet and outletsections and having the greater part thereof located in that part of theflue which lies adjacent the fire-box, the tubular portions constitutingsaid sections of said superheater element being so disposed in the fluethat certain contiguous tubular portions of diameters differing in onesense are positioned parallel to other contiguous portions of diametersdiffering. in" the opposite sense and so related to the diameters ofsaidcertain portions as to offset changes in the diameter of saidelement along the flue,

i 3. A superheater element for use in a flue of a smoke tube boilercomprising a plurality of interconnected, parallelly disposed tubularportions of different diameters extending forwardly and backwardly inthe flue and constituting an inlet section, an outlet section and aninterme-' diate section of smaller diameter than both said inletand'outlet sections and having the greater part thereof located in thatpart of the flue which lies adjacent the fire-box, the said sections ofthe superheater element being so positioned with respect to each otherinthe flue and the diameters of contiguous portions of diiferentdiameters being so related tothe diameters of other tubular portions.parallel thereto that theaggregat'e cross sectional area of parallellydisposed tubular portions is substantially the same at all points alongthe flue to provide a gas passage of substantially the same free crosssectional area along the flue,

4. A superheater element as recited in claim 1 characterized by the factthat the intermediate section includes at least one pair of parallellydisposed tubular portions that are interconnected by a return bendlocated in alignment with the transition between said intermediatesection and one of said other sections and which have diam-v eters sorelated to the tubular portions that are contiguous at said transitionas to offset the change in thediameter of said element at saidtransition.

5. A superheater element for use in a flue of a smoke tube boilercomprising a plurality of interconnected, parallelly disposed tubularportions of different diameters extending forwardly and backwardly inthe flue and constituting an inlet section, an outlet section and anintermediate section of smaller diameter than both said inlet and outletsections and having the greater part thereof located in that part of theflue which lies adjacent the fire-box, certain of said sectionsconsisting of a plurality of contiguous portions of different diameterspositioned in the flue to locate the transitions between certain of saidportions in alignment with the transitions between other tubularportions that are parallel thereto and which have diameters so relatedto those of said certain contiguous portions as to offset the change indiameter of said element between said contiguous portions at saidtransition.

6. A superheater element as recited in claim 5 characterized by the factthat said intermediate section includes pairs of parallelly disposedtubular portions that are interconnected by return bends at least one ofwhich is located in alignment with the transition between certain contiguous tubular portions of different diameters and the tubular portionsextending to and connected by said one return bend having diameters sorelated to the diameters of the tubular portions that are contiguous atsaid transition as to offset the change in the diameter of said elementat said transition.

7. A superheater element as recited in claim 5 wherein the intermediatesection consists of parallelly disposed tubular portions of differentdi- 1 ameters interconnected by return bends, with the return bendbetween at least one pair of its portions of said element that are ofdifferent diameters and the diameters of said pair of tubular portionsbeing so related to the diameter of tubular portions which arecontiguous at said transition as to oifset the change in diameter ofsaid element at said transition.

8. A superheater element as recited in claim 1 in which at least one ofsaid sections thereof comprises a plurality of contiguous portionsforming a single steam pathiand having cross-sectional areas ofdiiferent sizes increasing in diameter with respect to the direction ofgas flow through c 9. A superheater elementas specified in claim 1further characterized by the fact that each of its sections comprises aplurality of portions having cross-sectional areas of different sizes,contiguous portions of the inlet section decreasing in diameter andthose of the intermediate and outlet sections increasing in diameter,all with respect to the direction of steam flow through the superheaterelement.

10. A superheater element as specified in claim 1 further characterizedby the fact that said first section thereof comprises a plurality oftubes connected up in parallel to said intermediate section.

11. A superheater element as recited in claim 1 further characterized bythe fact that two of the three aforementioned sections thereof comprisea plurality of parallel tubes connected to the other section.

12. A superheater element as specified in claim 1 further characterizedby the fact that said first and said intermediate sections thereof eachcomprise a plurality of parallel tubes communicating with said lastsection of said element.

13. A superheater element as specified in claim 1 in which saidintermediate section thereof has the largest heating surface.

' v HERBERT FRANK.

